The present invention generally relates to an economizer for flash cooling a refrigerant liquid, and specifically with an economizer arranged coaxially with a condenser or other structure, e.g. an evaporator, for use in a refrigeration system having at least two stages of compression.
Refrigeration systems typically incorporate a refrigeration loop to provide chilled water for cooling a designated building space. A typical refrigeration loop includes a compressor to compress refrigerant gas, a condenser to condense the compressed refrigerant to a liquid, and an evaporator that utilizes the liquid refrigerant to cool water. The chilled water is then piped to the space to be cooled.
One such refrigeration or air conditioning system uses at least one centrifugal compressor and is referred to as a centrifugal chiller. Centrifugal compression involves the purely rotational motion of only a few mechanical parts. A single centrifugal compressor chiller, sometimes called a simplex chiller, typically range in size from 100 to above 2,000 tons of refrigeration. Typically, the reliability of centrifugal chillers is high, and the maintenance requirements are low.
Centrifugal chillers consume significant energy resources in commercial and other high cooling and/or heating demand facilities. Such chillers can have operating lives of upwards of thirty years or more in some cases.
Centrifugal chillers provide certain advantages and efficiencies when used in a building, city district (e.g. multiple buildings) or college campus, for example. Such chillers are useful over a wide range of temperature applications including Middle East conditions. At lower refrigeration capacities, screw, scroll or reciprocating-type compressors are most often used in, for example, water-based chiller applications.
One component of existing chillers is an economizer. The economizer improves the operating efficiency of the system.
An economizer is typically utilized between the condenser and the evaporator of a refrigeration system to cool refrigerant liquid below the temperature at which it leaves the condenser. Flash cooling is achieved by the evaporation of part of the refrigerant liquid as it flows from the condenser through nozzles, orifices, or other pressure reducing means into a chamber which is lower in pressure. The flashing refrigerant cools the remaining liquid by absorbing heat as it vaporizes. Upon separation from the cooled liquid, the refrigerant vapor, or flash gas, is conveyed to the inlet of a compressor stage operating at intermediate pressure. The cooled refrigerant liquid flows from the economizer to an evaporator, where it is vaporized in heat exchange relationship with another fluid, e.g., water, to satisfy a cooling load. Refrigerant vapor leaving the evaporator is typically compressed in two or more stages of compression. Prior economizers have been designed as separate units, distinct from the condenser, compressor and other structures common to chiller systems.
Prior chiller designs also typically connect the first stage discharge of a compressor to a second stage compressor and include complicated casting and piping arrangements. These designs are sometimes called two-stage, in-line designs.
Essentially, these in-line designs have a series of continuous castings that allow the discharge gas leaving a first stage compressor to be delivered into the inlet of the second stage compressor. The impeller of the first stage compressor imposes a great deal of tangential velocity to the fluid being compressed. This fluid with a tangential velocity is called swirling flow. As the fluid flows through the diffuser of the first stage compressor, it passes through a 180° U-bend. A set of blades in the return channel bend are typically used in an attempt to direct the fluid flow in an axial direction at the inlet to the second stage compressor. This swirling fluid flow is combined with the flash gas flow from the economizer to essentially inter-cool the swirling gas of the first stage compression. In practice, the mixing of the two flows is not as thorough as desired and predominately occurs far enough down the fluid flow path, e.g. in the impellers of the second stage, that only a modest efficiency improvement is gained.